servlet拦截器代码

1-
实现Servlet.Filter接口
public class AdminLoginFilter implements Filter


新建一个实现filter接口的类,实现dofilter方法，在dofilter方法里面写一个判读，比如如果用户名密码为空，则返回到登录页面
public class TestFilter  implements Filter  { 
public void doFilter(ServletRequest srt, ServletResponse sre,
   FilterChain filterChain) throws IOException, ServletException {
 
  HttpServletRequest request = (HttpServletRequest)srt;
  HttpServletResponse response = (HttpServletResponse)sre;
 
  String name= (String)request.getSession().getAttribute("name");
 
  if( name== null || name.trim().length() < 1) {
 
  
   response.sendRedirect( "/denglu.jsp" );
  }else {
   filterChain.doFilter(request, response);
  }
}


web.xml配置过滤器
  <filter>
   <filter-name>TestFilter  </filter-name>
   <filter-class>/test/TestFilter  </filter-class>
  </filter>

配置多个映射，哪些请求执行过滤器
  <filter-mapping>
   <filter-name>TestFilter  </filter-name>
   <url-pattern>/web-inf/test/*</url-pattern>
  </filter-mapping>
  <filter-mapping>
   <filter-name>TestFilter  </filter-name>
   <url-pattern>/login.do</url-pattern>
  </filter-mapping>

  <filter-mapping>
   <filter-name>TestFilter  </filter-name>
   <url-pattern>/loginin.do</url-pattern>
  </filter-mapping>